There are an enormous number and volumetric quantity of natural and man-caused hydrocarbon contaminations of soil. The most common of these are accidental or deliberate spills of gasoline, oils and greases, kerosene, diesel fuels and aircraft fuels. These sites range from oil field operations to aircraft refueling sites, gas stations and grease dumps. There are also natural oil seeps, and earthquake, construction or slide-induced ruptures of gas and oil lines.
The problem is enormous: For example, in the State of California alone there are some 12,000 sites involving 63 million tons of soil that needs to be remediated. The problem is severe as the transfer of real estate in excess of $50,000 requires a soil survey in order to determine the nature, extent and degree of hydrocarbon contamination. If there is any contamination, then the law mandates that the soil be remediated.
The current state of the art is not to remediate raw, contaminated soil, but rather simply to encapsulate it without pretreatment in some other material as a component, such as a component of asphalt. Other uses have been proposed, such as encapsulating in concrete, soilcrete and the like. However, the quantity of soil involved and the current state of encapsulation techniques yields only low grade, light duty mixes. For example, asphalt-encapsulated non-pretreated soil is low grade and may only be used for parking lots and driveways. It cannot be used as high grade asphalt for roads, runways or heavy traffic access ways.
The patent literature shows a variety of approaches to reconditioning soils contaminated by crude oil or other refined petroleum products. Broadly these involve indirect thermal treatment, aeration, bioremediation involving microbial action, and chemical treatment. For example, Noland U.S. Pat. No. 4,738,206 seals soil in a stripping conveyor against contact with air (low O.sub.2 content), and indirectly heats the soil in the conveyor by contact with hollow screw flights heated by hot transfer fluid. The hot transfer fluid may be hot oil heated externally of the conveyor by a fuel fired heater. The exhaust gases of the heater are non-oxidizing and fed into the conveyor countercurrent to the soil feed. The conveyor is heated to between 120.degree.-450.degree. F., with 140.degree.-220.degree. F. being preferred. The hot gases exhausting the conveyor are first passed through a baghouse, then to a condenser apparently without heat recovery, and then a gas/liquid separator. The gases then go to an afterburner where they are incinerated.
Giguere U.S. Pat. No. 4,424,081 involves an aqueous system of mixing and heating the contaminated soil to form a blended slurry. A sparger kiln agitates the aqueous slurry to break down the component parts into a fine particle slurry. The fine particle slurry is then washed in a clarifier, and further washing is done with aid of reagents in flotation cells which also separate oil from the fine soil particles. An aeration clarifier separates oil from the liquid mixture removed from the flotation cells.
Honour U.S. Pat. No. 4,170,551 burns waste oil on board ship in the ship's steam boiler. Jennings U.S. Pat. Nos. 4,828,030 and 4,787,452 dispose of fines produced with high viscosity oil by mixing with hydraulic fracturing fluid or steam, which mixture is used a fracing fluid.
Bastian et al in U.S. Pat. No. 4,745,850 employs aeration in Situ et al by providing a series of vertical boreholes and horizontal conduits connecting the boreholes to provide an airpath. Suction is provided by a conventional wind turbine.
Brown U.S. Pat. No. 4,515,684 reclaims oil from emulsified mixtures of oil, water and particulate solids by using one or more special settler(s) having an internal mixing centerwell and means for heating or cooling therein, and employing chemical demulsifying agents. Bruya U.S. Pat. No. 4,841,998 employs an aqueous ammonia solution in a soil agitator and settling tanks to treat soil having organic hazardous wastes. The contaminants best treated by this method are polynuclear aromatic hydrocarbons, other non-polar organic wastes, and petroleum products.
Globus U.S. Pat. No. 4,581,130 treats chlorinated hydrocarbons, including PCBs by dispersing sodium metal in oil, reacting with copper and lead to form a ternary alloy of Na/Cu/Pb, contacting the halogenated hydrocarbon with the alloy, and recovering sodium chloride, excess alloy and Cu/Pb from the now halogen-free material. Crisman et al U.S. Pat. No. 4,447,332 separates volatile liquid hydrocarbons and/or water from fuel sludge by filtration and exposure to UV radiation (light) to detoxify lead-containing fuel storage tank sludge.
Various asphalt processes and equipment used in asphalt plants are shown in Bracegirdle et al Patent Nos. 4,784,216; 4,245,915; 4,378,162 and Re 32,206. None are directed to soil remediation. 4,784,216 shows a R.A.P. heater which may be used as one element, a condenser/heat exchanger, of the system of the present invention. 4,245,918, 4,378,162 and Re 32,206 show various aspects of making asphalt in a sealed, indirectly heated mixing chamber.
Various patents show use of heat to recover hydrocarbons from oil shale, tar sands and coal, typically at very high temperatures, some of which include cracking. For example, Weichman, U.S. Pat. No. 4,133,741 recovers shale oil hydrocarbons from oil shale in a continuous, straight or circular horizontal moving bed retort of cross-flow design to prevent condensation and revaporization present in the usual oil shale vertical furnace retorts. The Weichman process uses neutral or reducing gas at temperatures of 800.degree.-1100.degree. F. in a down flow direction through the bed of crushed oil shale rock. No examples are shown in this theoretical patent, and no outlet spent shale hydrocarbon content is disclosed. Duncan U.S. Pat. No. 4,585,543 recovers hydrocarbons from oil shale, coal or tar sands by thermal regenerative cracking in a vertical reactor at a temperature on the order of 1400 with residence time of 0.005-2 sec. The solids go to a stripper and thence to a gasifier. Rammler U.S. Pat. No. 4,659,456 directly contacts tar sands, oil sands and diatomite with superheated steam at 200.degree.-750.degree. C., with the remaining solids going to dry distillation at 400.degree.-600.degree. C. by mixing with a fine grained heat transfer medium. The residue may contain residual hydrocarbons.
None of these three oil shale/tar sands patents are directed to the same problem of soil remediation, with near zero discharge, and their process conditions and outputs are vastly different, as the spoil pile residues from oil shale and tar sands processing are usually above 3% hydrocarbons, i.e. are still very contaminated with hydrocarbons.
Accordingly, there is an immediate and significant need for a process which remediates soil contaminated by these types of hydrocarbons to yield a variety of remediated products, some suitable for safe reemplacement, others for roadbed fill, and still others as a component of high grade asphalt.